1. Field of the Invention
This invention relates to a surface emitting device and a liquid crystal display device including the surface emitting device.
2. Related Art
A surface emitting device that realizes surface emission of light from light emitting diode (LED) chips serving as point light sources has been used as a light source of a liquid crystal backlight or the like. The surface emitting device has such a structure that light from one or more light emitting diodes is caused to enter a light guide plate having a pair of main surfaces opposed to each other through an end surface thereof, and the light is emitted from the entirety of one of the main surfaces of the light guide plate.
In the above-mentioned surface emitting device, it is important to output light uniformly from a light outgoing surface thereof, and hence there have been proposed various structures for realizing the uniformity of the output light (see Japanese Unexamined Patent Application Publication (JP-A) No. 2001-28203).
With reference to FIGS. 12 to 14B, an example of the surface emitting device is described.
As illustrated in FIGS. 12 to 14B, the surface emitting device includes: a light guide plate 910 having a light outgoing surface 913 and a reflection surface 911 opposed to each other; a reflection sheet 920 formed on the reflection surface 911 of the light guide plate 910; and an LED (light emitting diode) light source 930 that includes at least one LED (light emitting diode) element and is provided so that light from the LED element enters the light guide plate 910 through one end surface 912 of the light guide plate 910. The light that enters the light guide plate 910 is emitted from the light outgoing surface 913 of the light guide plate 910. The light guide plate 910 includes a light diffusion portion 914 formed in the one end surface 912, and the light diffusion portion 914 is recessed so as to diffuse the light from the LED light source 930 inside the light guide plate 910. In addition, the light diffusion portion 914 is formed so that an upper end of the light diffusion portion 914 is made apart from the light outgoing surface 913 on the one end surface 912 (FIG. 14B). It should be noted that the light outgoing surface of the light guide plate is a surface from which light is emitted and the reflection surface thereof is a surface located on the opposite side to the light outgoing surface.
In order to cause the light outgoing surface 913 of the light guide plate 910 to efficiently emit light of the entering light, the light diffusion portion 914 is preferred to include a plurality of cutouts that are each formed by cutting out the one end surface 912 into a half pyramidal or half circular conical shape defined from one point (as a vertex) apart from the light outgoing surface 913 toward the reflection surface 911 as illustrated in FIG. 13.
As described above, in the surface emitting device of FIG. 12, the light diffusion portion 914 including the plurality of cutouts each having a half pyramidal or half circular conical shape is formed in the light incoming end surface of the light guide plate 910. Accordingly, the light emitted from the LED light source 930 is diffused by the light diffusion portion 914 as schematically illustrated in FIG. 14A and enters the light guide plate 910, to thereby enhance the uniformity of emitted light brightness on the light outgoing surface 913 of the light guide plate 910.